The streaming technology is a technology which can transfer multimedia data streams over IP network. In the traditional play technology, the client downloads a complete file from the server for playing. The streaming technology utilizes streaming transmission, divides the whole multimedia file into multiple compressed packets, and transmits the compressed packets to the client sequentially in real time. The user may decompress the arriving packets while downloading subsequent compressed packets, thus saving time. With the development of computer technologies, the streaming technology is more and more widely applied to Video On Demand (VOD). The VOD technology converts a recorded video program into a digital video file directly playable on a computer through a series of processes such as capture and compression, and stores the file on a web server, thus being available for users. The user watches the video and audio programs of the video service provider through a terminal device, and can play the program forward, backward, or pause the program while watching the program. VOD service is characterized by celerity, convenience and interaction. With the increase of network bandwidth, the VOD service is more and more promising. The development of the Internet Protocol Television (IPTV) spurs the popularity of applying the streaming technology.
When the VOD media data are transmitted in IPTV system, the traditional streaming system exposes many problems. The VOD imposes an excessive impact on the server of the IPTV, which tends to cause a single-point failure. Therefore, a Content Delivery Network (CDN) technology is introduced. The essence of the CDN technology is to push the content from the center to the edge nearby the user, thus effectively improving the Quality of Service (QoS) of the content and relieving the pressure on the central devices and backbone networks. Through the CDN technology, the content service changes from a single central structure to a distributed structure. When the user clicks the program, the desired media content can be obtained from the edge server nearby the user. The user obtains resources from the same edge server when playing fast forward/backward and jumping forward/backward.
With the rapid development of the Peer-to-Peer (P2P) technology in recent years, the P2P technology is more and more applied to the streaming service, for example, the P2P-based streaming software such as PPLive and PPStream. By virtue of the characteristics of the P2P, the user node acts as a server for providing contents and sharing the load of servers, thus enhancing the extensibility of the system and making the media data more distributed. In the current streaming system based on P2P, each node sends the received content to other nodes while receiving the content. Therefore, the content provided by each node to other nodes varies with the content watched by the node. Consequently, in order to create a TCP connection, the user has to search for the corresponding program source again while playing the media fast forward/backward, or jumping forward/backward.
FIG. 1 is a schematic diagram of PPLive streaming software. When the user drags the progress bar of the media during play, the user needs to query the user list on the central server first, and then creates a corresponding TCP connection with the relevant node to play the media according to the current play conditions. This prolongs the delay of playing the media, and disregards the proximity between nodes. Meanwhile, the central server needs to keep updating the content provided by each node, thus increasing the load of the central server. Moreover, each user node stores only a small portion of media contents. In this case, if a user wants to access a complete program, the user has to access multiple user nodes before obtaining the complete resources. When the user plays fast forward and fast backward or drags the progress bar, the user may need to span different nodes which provide program contents, search for the program source again and create a TCP connection, which further prolong the delay of playing the media.
After the user drags the progress bar of the media in a CDN-based network, the user still obtains the resources from the same server, and does not need to search the server again or create a TCP connection. Therefore, the play delay is about 2-3 seconds. However, after the user drags the progress bar in a P2P-based network, the user needs to search the server again and create a TCP connection, and the play delay is over 5 seconds if the buffer time of play is considered, which is unacceptable to the user.